Friday, November 25, 2016

Antarctic sea ice had barely
changed from where it was 100 years ago, scientists have discovered,
after poring over the logbooks of great polar explorers such as Robert Falcon Scott and Ernest Shackleton.
Experts were concerned that ice at the South Pole had declined
significantly since the 1950s, which they feared was driven by man-made
climate change.
But new analysis suggests that conditions are now virtually identical
to when the Terra Nova and Endurance sailed to the continent in the
early 1900s, indicating that declines are part of a natural cycle and
not the result of global warming.

Scott's ship the Terra Nova

It also explains why sea
ice levels in the South Pole have begun to rise again in recent years, a
trend which has left climate scientists scratching their heads.
"The missions of Scott and Shackleton are remembered in
history as heroic failures, yet the data collected by these and other
explorers could profoundly change the way we view the ebb and flow of
Antarctic sea ice,” said Dr Jonathan Day, who led the study, which was
published in the journal The Cryosphere.

The Endurance, trapped in sea ice

"We know that sea ice in the Antarctic has increased
slightly over the past 30 years, since satellite observations began.
Scientists have been grappling to understand this trend in the context
of global warming, but these new findings suggest it may not be anything
new.
"If ice levels were as low a century ago as estimated in
this research, then a similar increase may have occurred between then
and the middle of the century, when previous studies suggest ice levels
were far higher."

Captain Scott and team

The study was based on
the ice observations recorded in the logbooks from 11 voyages between
1897 and 1917, including three expeditions led by Captain Scott, two by Shackleton, as well as sea-ice records from Belgian, German and French missions.
Captain Scott died
along with his team in 1912 after losing to Norwegian Roald Amundsen in
the race to the South Pole, while Shackleton's ship sank after becoming
trapped in ice in 1915 as he and his crew attempted the first land
crossing of Antarctica.
The study is the first to calculate sea ice in the period
prior to the 1930s, and suggests the levels in the early 1900s were
between 3.3 and 4.3 million square miles (5.3 and 7.4 million square
kilometres)
Estimates suggest Antarctic sea ice extent was significantly
higher during the 1950s, before a steep decline returned it to around
3.7 million miles (6 million square kilometres) in recent decades which
is just 14 per cent smaller than at the highest point of the 1900s and
12 per cent bigger than than the lowest point.

One of the
first aerial photographs of the Antarctic obtained from a balloon in
1901, showing Erich Von Drygalski's ship The Gauss

The findings demonstrate
that the climate of Antarctica fluctuated significantly throughout the
20th century and indicates that sea ice in the Antarctic is much less
sensitive to the effects of climate change than that of the Arctic, which has experienced a dramatic decline during the 20th century.
In future the team plans to use data from naval and whaling
ships as well as the logs from Amundsen’s expeditions to complete the
picture.
Separate research by the British Antarctic Survey also
showed that the present day loss of the Pine Island Glacier on the West
Antarctic Ice Sheet has been happening since the mid 20th century and
was probably caused by El Nino activity rather than global warming.
Pine Island Glacier, which drains into the Amundsen Sea in
West Antarctica, is retreating and thinning rapidly, but the initial
triggering mechanism was unclear.
The team looked a sediment cores in
the area which showed that an ocean cavity under the ice shelf began to
form around 1945, following a pulse of warmth associated with El Niño
events in the tropical Pacific Ocean.
“We are very excited about this new finding as it provides
the first direct evidence of the timing of glacier retreat even before
we had satellites to measure them,” said lead author, marine geologist
Dr James Smith from British Antarctic Survey.
“They show us how changes half-way across the planet in the
tropical Pacific, reached through the ocean to influence the Antarctic
ice sheet.”
Co-author Professor Bob Bindschadler of NASA added: “A
significant implication of our findings is that once an ice sheet
retreat is set in motion it can continue for decades, even if what
started gets no worse.
“It is possible that the changes we see today on Pine Island Glacier were essentially set in motion in the 1940s.”
The Pine Island research was published in Nature.